Engine starting problem

[BlueChip]

The starter on my Yanmar 40hp engine was reluctant to turn it over at the weekend, however on switching the battery selector to both, the engine turned over and started fine.
On checking the engine starting battery (new 2008) I found it to be fully charged as shown by the magic eye.
The boat is left permanently on charge, so there is no reason to doubt the battery was anything other than fully charged, the engine battery and battery selector switch connectors are all secure as is the connector to the starter motor. The starter battery is only used for that purpose.
Any suggestions anyone?

 

[VicS]

Double check that the starter battery connections are clean and tight and also the connection from it to the change over switch.

If you have one of those rotary 1, 2, both, off switches it must be a suspect.

Not so sure about those magic eyes, don't they only indicate the state of one cell.

Check all the cells with a hydrometer if possible, if not the check the volts after it has rested with no charge or discharge for 12 hours.

12.8v excellent, fully charged; 12.6-12.7 good, nearly fully charged; 12.5 OK; below 12.5 iffy; 12.2 ish only half charged.

Even if the voltmeter or hydrometer shows it as Ok it does not guarantee that it can supply the high current required for starting. Removal for professional testing may be necessary. but if it is brand new and the volts/ hydrometer show it to be fully chaged it is most likely to be a poor connection somewhere.

 

[rob2]

Stating the obvious, I know - if the cell's low on electrolyte, then the magic eye will give a false reading. With the battery on permanent charge, that could easily happen.

 

[mtb]

see if you can borrow a rapid discharger to test the battery under load
the rest has been said

cheers
mick

 

[VicS]

re Magic eyes.
I have not had much to do with them but I thought they gave different indicatios for charged, not charged or low on electrolyte

 

[Oldhand]

[ QUOTE ]
If you have one of those rotary 1, 2, both, off switches it must be a suspect.

[/ QUOTE ]

Whatever the battery switch, check the resistance between the input and ouput terminals, should be 0 ohms. I had a switch showing 2 ohms and it was causing starting problems. The switches that use a bayonet type key have no wiping action on the contacts and are thus more susceptible to becoming high resistance. The most overlooked critical wiring connection is, I suggest, the negative or earth connection to the engine so make sure that is clean and corrosion free as well as everything else.